Facing a government shutdown at the end of the week, GOP and Democratic leaders have made little progress on finalizing a massive omnibus spending package they had hoped to introduce by Monday.

While senior Republicans are confident they will reach an agreement on the yearlong funding measure at some point, it appears increasingly likely that no deal will be in place by the Friday Dec. 11 deadline, meaning a short-term spending bill will have to be enacted in order to avoid a repeat of the 2013 shutdown. And without a compromise to present on Monday, members and senators have a tense week ahead as Congress rushes to complete its year-end work and depart for the holiday season.

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Senior aides in both parties say Republican leaders offered their Democratic counterparts a new funding proposal last Friday, but the latest offer produced no breakthrough and both sides continued negotiations through the weekend while making little headway. The two sides are hashing out policy riders covering Syrian refugees, environmental policy and oil exports, among other issues.

Staffers for the Appropriations committees worked throughout the weekend on the funding measure. A senior Democratic aide said staffers have been working until midnight and there are “hours and hours of talks going on each day.”

Staff on the GOP side were on the Hill until late Saturday evening, as well. “We are continuing to negotiate. We expect to have a bill ready for the floor next week,” said Jennifer Hing, spokeswoman for House Appropriations Committee Chairman Hal Rogers (R-Ky.).

The long hours show how much both sides want to avoid a government shutdown. Speaker Paul Ryan (R-Wis.), whom GOP lawmakers elected only a month ago to lead the House, is steadfast that the funding debate will be settled without any repeat of 2013, when the federal government shut down for 16 days.

But both sides were still battling over policy riders as of Sunday afternoon. House and Senate Democrats, as well as the White House, have long said they won’t accept any “poison pill” riders to the government-spending package. However, Ryan will need some of those very same policy riders to attract wary Republicans to vote for the the deal as a majority of GOP House lawmakers are opposed to the measure’s overall spending limits — which were hammered out by former Speaker John Boehner (R-Ohio) before he retired.

Republicans also want to see the omnibus bill tackle the contentious issue of Syrian refugees. The House already adopted a bill last month to toughen vetting standards for individuals from Syria and Iraq hoping to enter the U.S. as refugees. However, the Senate didn’t take up that bill, and supporters believe the omnibus is the best vehicle to revise those standards.

Some Republicans also want to see funds cut off for refugee relocation — a move close to 100 House Democrats are protesting.

“We should all agree that inserting wholesale changes to refugee admission policies into a year-end spending bill — where they cannot be properly debated or amended — is not the appropriate way to consider these issues,” states a letter sent by House Democrats.

Beyond Syria, there will also be questions about how far Senate Democrats will push new gun control measures in the wake of a shooting in San Bernardino, California, that left 14 dead and 21 injured. The FBI is now investigating those murders — carried out by Syed Farook and Tashfeen Malik — as an “act of terrorism.” Farook and Malik were killed in a shootout with police. Farook was a U.S. citizen, while his wife was born in Pakistan and recently lived in Saudi Arabia.

President Barack Obama had an Oval Office speech Sunday night to address the San Bernardino shootings, which came amid high-profile terrorist attacks in Paris and elsewhere. Republican presidential nominees have seized on the shooting to call for barring new refugees from some countries. Obama and the Democrats have so far resisted such calls.

There are also ongoing negotiations over a huge package of expiring tax breaks — dubbed tax extenders on the Hill — that has a price tag running into the hundreds of billions of dollars. Those talks have been elevated to senior leadership levels, yet there is still ongoing debate over energy, oil and health provisions. The extenders expired at the end of 2014, but lawmakers can retroactively pass the bill. Business groups are strongly pushing the package, which includes a research and development credit favored by Silicon Valley.

One of the main holdups is that Democrats — especially House Minority Leader Nancy Pelosi of California — want to “index” for inflation provisions aimed at families. Republicans have countered that they would support such a move only in return for ensuring the “integrity” of such programs, such as providing Social Security numbers for families seeking to use a child tax credit. So far, Democrats have said no.

And as the cost of the tax extenders package has swelled to as much as $800 billion by some estimates, lawmakers in both parties have objected that it has become too costly. With that hefty price tag in mind, negotiators may opt to extend many of the tax breaks for two years, rather than permanently.

There is some discussion of attaching the extenders package to the omnibus to ease passage of the government-funding bill. A notice sent to lawmakers from Majority Leader Kevin McCarthy’s office over the weekend said votes on the tax and funding bills were possible but lawmakers should keep their schedules’ flexible.

But that means a jam-packed voting schedule in the House. Beyond the extenders and the government funding bill, lawmakers also want to vote on changes to a visa-waiver program to make it harder for individuals from certain countries to enter the U.S. if they’ve been to Syria, Iraq, part of Africa or other areas where there are strong jihadist movements.

The funding bill will be a key moment for Ryan. He’ll need to win Republicans’ support for the spending bill without looking as if he’s giving away too much to Democrats — a perception that eventually cost Boehner his job.

The funding melee comes just as Ryan is trying to refocus the Republican Party after years of disarray in the House have forced lawmakers to the brink on many must-pass bills.

“I mean, show what we would do, what our ideal policy would be — looking forward to 2017 and beyond. We owe it to the country to offer a bold, pro-growth agenda,” Ryan said Thursday. “Our No. 1 goal for the next year is to put together a complete alternative to the left’s agenda.”

But Ryan will have to wrestle with his right flank, just as Boehner did. Members of the House Freedom Caucus have steadfastly insisted that to get any broad support from their 40-member group, the omnibus will have to include language on Syria and three policy riders on Planned Parenthood that were offered by the Pro-Life Caucus. However, including those provisions would end any chance of Democratic support and draw a veto threat from the White House.